Heterotypic Current Transformer Design for Overcurrent Protection of SiC MOSFET

Overcurrent protection of silicon carbide (SiC) MOSFETs plays a critical role in the medium voltage (MV) applications to avoid severe damage to the hardware, and there are more challenges because of the much higher insulation voltage required and the faster switching speed of SiC devices. To measure the power device switching current under these harsh conditions, highly integrated, compatible, and strongly insulated current sensors became the major technological breakthroughs to be solved. This paper presents a heterotypic current transformer design with strong compatibility and high insulation to realize overcurrent protection. A ferrite rod wound with copper wires is placed into a vertical bar Omega shape current conductor tube. This solution can be easily integrated into bus bars or power modules. The modeling analysis and design considerations of Omega-shape copper tube are discussed. The high insulation capability was realized by encapsulating the current transformer into the high dielectric strength silicone gel. Experimental Hi-Pot test proves the insulation capability up to 5 kV. Additionally, a double pulse test is carried out to evaluate the proposed current sensor performance, which can realize 72.3ns fast response including 16ns detection time and 56.3ns action time for overcurrent protection of SiC MOSFETs.